Book Image

Template Metaprogramming with C++

By : Marius Bancila
Book Image

Template Metaprogramming with C++

By: Marius Bancila

Overview of this book

Learn how the metaprogramming technique enables you to create data structures and functions that allow computation to happen at compile time. With this book, you'll realize how templates help you avoid writing duplicate code and are key to creating generic libraries, such as the standard library or Boost, that can be used in a multitude of programs. The introductory chapters of this book will give you insights into the fundamentals of templates and metaprogramming. You'll then move on to practice writing complex templates and exploring advanced concepts such as template recursion, template argument deduction, forwarding references, type traits, and conditional compilation. Along the way, you'll learn how to write variadic templates and how to provide requirements to the template arguments with C++20 constraints and concepts. Finally, you'll apply your knowledge of C++ metaprogramming templates to implement various metaprogramming patterns and techniques. By the end of this book, you'll have learned how to write effective templates and implement metaprogramming in your everyday programming journey.
Table of Contents (16 chapters)
Part 1: Core Template Concepts
Part 2: Advanced Template Features
Part 3: Applied Templates
Appendix: Closing Notes

Defining concepts

The constraints seen previously are nameless predicates defined in the places they are used. Many constraints are generic and can be used in multiple places. Let’s consider the following example of a function similar to the add function. This function performs the multiplication of arithmetic values and is shown next:

template <typename T>
requires std::is_arithmetic_v<T>
T mul(T const a, T const b)
   return a * b;

The same requires clause seen with the add function is present here. To avoid this repetitive code, we can define a name constraint that can be reused in multiple places. A named constraint is called a concept. A concept is defined with the new concept keyword and template syntax. Here is an example:

template<typename T>
concept arithmetic = std::is_arithmetic_v<T>;

Even though they are assigned a Boolean value, concept names should not contain verbs. They represent requirements and are used...